The present invention relates to a drilling tool for the chip-breaking machining of metallic materials, especially for so-called ejector drilling. However, it may also advantageously be used for so-called BTA-drilling.
It is known to use cutting inserts of cemented carbide for drills, which inserts are fastened by mechanical fastening arrangements, the inserts being provided with one or more recesses in the chip surface for chip-breaking purposes. Such drills are, for instance, known from U.S. Pat. No. 4,215,957. However, it has turned out to be difficult to attain an optimal forming of the chips. That is, it has been impossible to attain the desired short, comma-shaped chips, at the same time as it has been impossible to reduce power consumption when running the drill in the desired way. Further, sometimes the chip canals, which conduct the chips to a central discharge hole, have turned out to be too narrow for the created chips, which has resulted in a chip stoppage and jamming.
Further, in U.S. Pat. No. 5,302,060 drilling tool is described comprising a drill body on which two or more cutting inserts are mounted. The inserts are substantially formed as trapezoids and are axially mounted, i.e., the abutment surfaces of the cutting inserts extend axially, the inserts suitably being fixed by brazing. However, after a certain time of wear, also this drill body has sometimes caused chip jamming in the area where the two chip canals and the central hole meet. Moreover, the drill body consists of two parts which are joined by welding, namely the drill head or crown, and the cylindrical, threaded shaft part. This weld joint in combination with the fact that the drill crown has been cast, has frequently resulted in an imperfect roundness of the final product. This has in turn caused customers to require that a finishing grinding be performed in order to attain a perfect roundness and rotation symmetry around is the central axis, which unnecessarily increases the production cost of the drill. A further drawback of this weld joint has turned out to be that chips occasionally get stuck in the weld joint, since in practice a weld joint leaves a certain gap on the interior side. Sometimes, even if only a single chip gets wedged in that gap, the following chips can pile up and cause chip jamming and, in a worst case, a tool breakdown.
Thus, a primary object of the present invention is to provide a drill body, particularly a drill body for ejector drilling, that practically eliminates any risk of chip jamming.
A further object of the present invention is to eliminate any unevenness on the inside of the drill body, in which a chip could get jammed.
Another object of the present invention is to provide a drill body with practically perfect external roundness.